Continuing work using calcium stable isotonic tracers for the measurement of absorption, distribution and excretion of calcium have led to a number of clinically significant findings. 1) Calcium metabolism in 5 adolescents with anorexia nervosa (age 17.0 +/-2.2 yrs, wt 36.1 +/-6.7 kg) showed reduced absorption, increased urinary calcium excretion and negative calcium retention compared to healthy adolescent females (age 14.0 +/-1.7 yrs., wt 57.1 +/-11.5 kg - mean +/- SD). Patients with anorexia nervosa consumed 1650 mg/day calcium and absorbed 215+/-55 mg/day, excreted 252+/- 73 mg/day in urine leading to a net retention of -36+/-74 mg/day. The healthy girls consumed 1000 mg/day Ca and absorbed 427+/-53 mg/day, excreted 143+/-41 mg/day in urine and had a net retention of 284+/-94 mg/day. The differences between the patients with anorexia nervosa and healthy subjects may be a consequence of the elevated cortisol levels in the former [See project ZOI HD 01400-07 LTPBI. 2) Calcium metabolism studies in 6 premature infants (1.4+/-0.3 kg BW, 19+/-12 days age at study) fed premature infant formula and consuming 214+/-15.1 mg/kg/day Ca had absorbed 138.1+/-33.7 mg/kg/day, excreted 2.8 mg/kg/day in urine and endogenous fecal excretion of 17.1 mg/kg/day and had net retention of 118.3+/-38.2 mg/kg/day. These values demonstrate calcium retention comparable to in utero levels. 3) Studies of calcium distribution in Cynomolgus monkeys (ages 35-38 mos) before and after 6 wks of testosterone administration showed significant increases in growth velocity (0.107+/- 0.003 to 0.353+/-0.20 mm/wk, p=0.001), mass of calcium in the rapidly turning over pool (22.3+/-10.3 to 63.7+/-24.3 mg. p<0.01) after administration of testosterone. This hormone may increase the availability of calcium in the rapidly turning over pool and thereby alter growth rate.